Belt-tensioning mechanism



Nov. 3, 1959 H. c. HANKS 2,910,879

BELT-TENSIONING MECHANISM Filed Oct. 3l, 1957 2 Sheets-Sheet 1 Har/rg C. Hanlf,

BY?r ,r

ATTORNEYS Nov. 3, 1959 H. c. HANKS 2,910,879

BELT-TENSIONING MECHANISM Filed Oct. 3l, 1957 2 Sheets-Sheet 2 2G zw INVENT OR Har/q C. Han

BY? W ATTORNEYS BELT-TENSIONING MECHANISM Harry C. Hanks, North Madison, Conn.

Application October 31, 1957, Serial No. 693,657

4 Claims. (Cl. 741-242.14)

This invention relates to a belt-tensioning mechanism, and relates more particularly to a mechanism for maintaining adequate belt tension by compensating for belt stretch and load transmitted irrespective of the direction of rotation of the belt.

One object of the invention is to provide, in a belttensioning mechanism, an improved control system for controlling the movement of a carriage which may support a belt-driving motor or a belt-driven instrumentality, the position of the carriage governing the tension on the belt.

Another object of the invention is to provide a fully automatic control system in a belt-tensioning mechanism.

Still another object is to provide in a belt-tensioning mechanism such as characterized above, motor-driven screw means for effecting movement of the carriage.

Further objects of the invention will appear from the following detailed description of one form of the belttensioning mechanism illustrated in the drawings by way of example.

In the drawings:

Fig. l is a fragmentary top plane view illustrating diagrammatically a belt-tensioning mechanism embodying the invention and showing the same in association with an electric motor mounted on the mechanism and driving an instrumentality through an endless belt;

Fig. 2 is an enlarged top plan view of the mechanism with the motor removed;

Fig. 3 is a similar view showing the mechanism in side elevation;

Fig. 4 is a sectional view taken on line 4-4 of Fig. 2;

Fig. 5 is a sectional view taken on line 5--5 of Fig. 2;

Fig. 6 is an enlarged sectional View taken on line 6-6 of Fig. 2; and

Fig. 7 is a diagrammatic view of the control system.

In Fig. 1 there is illustrated more or less diagrammatically, an electric motor lil, which may be reversible, driving a pulley 13. A driven instrumentality is indicated in this view at 12., the instrumentality having a pulley 13a. A belt 14 is trained over the pulleys 13, 13a. As 4shown in Fig. l, the motor 10 is supported on a rectangular carriage, indicated generally at 11, mounted for reciprocating movement in a direction to tighten or slacken the belt 14. However, if desired, the motor may have a stationary mounting and the driven instrumentality may be mounted on the carriage.

` As shown in Fig. 2, for example, the carriage-supporting mechanism includes a substantially fiat horizontally elongated bed 15 having at each side thereof a pair of longitudinally spaced and upstanding lugs 16. A pair of rails 17 is provided, the rails extending along the respective sides of the bed 15, each rail 17 extending between and being supported by one pair of the lugs 16. The rails 17, which are of cylindrical form and which support the carriage 11, are fixed to the respective lugs 16 in upwardly spaced relation from the bottom of the bed 15. The bed 15 is also provided with a pair of longitudinally spaced upwardly extending lugs 18. As shown in Fig. 2,the pair of lugs 18 is spaced approximately midnited States Patent 'ice way between the pair of lugs 16 and a screw 19 extends through the lugs 18 and is journaled therein.

The carriage 11 has a plate-like top 21 and is provided with integrally formed sides 22 which extend downwardly over the respective rails 17. Integral with the sides 22 are inwardly extending flanges 23 in opposing relation to one another. The flanges 2'3 extend underl the respective rails 17, as shown in Fig. 5. The carriage is provided with two pairs of rollers 25 disposed inwardly of the rails 17, each pair of rollers bearing against one of the rails 17. Each roller 25 has its periphery formed to correspond to the curvature (see Fig. 5) of the corresponding rail 17 and is mounted on a stub shaft 26 extending through the plate-like top 21 of the carriage and the corresponding flange 23. Suitable antifriction devices 27 (Fig. 5) may be interposed between each stub shaft 26 and the corresponding roller 25. As shown in the last-mentioned view, the rollers 25 may be rather closely confined between the plate-like top 21 of the carriage and the corresponding fianges 23. It will be understood that the rollers 25 serve not only as anti-friction members but also serve to inhibit twisting or angular dislocation of the carriage owing to their disposition adjacent the respective corners of the latter, as shown in Fig. 2. To further inhibit friction between the carriage 11 and the rails 17, and also to serve as load-bearing members, plug-like inserts 27a may extend through the plate-like top 21 of the carriage adjacent the four corners thereof to bear against the tops of the respective rails, the inserts 27a preferably being formed of nylon. The inserts 27a extend below the plate-like top 21 and the arrangement is such that top 21 is spaced upwardly from the rails 17 by the inserts.

As shown in Fig. 2, the top 21 is provided with a plurality of openings 21a through which suitable fasteners may extend to secure the motor to the top. As shown in Fig. 5, two lugs 28 are suspended from the underside of the top 21 in laterally spaced-apart relation, the lugs being disposed in what may be referred to generally as the central (see Fig. 2) region of the carriage. A pair of fluid pressure devices 29 are provided, each liuid pressure device cooperating with one of the lugs 28. The fluid pressure devices 29 are carried at the respective ends of a nut member 30 elongated transversely of the bed 15 and cooperating with the threads of the screw 19. As shown in Fig. 5, the screw 19 extends through the nut member 30 midway between the last-mentioned ends of the latter, and the nut member is engaged by the bed 15 (Fig. 5) to prevent rotation of the member when the screw 19 is rotated. Each fiuid pressure device 29 carried by the member 3l) is constituted by a piston member 32 engageable with one of the lugs 28 and extensible from a hydraulic cylinder 33. Each fiuid cylinder is suitably fixed to the nut member 30 so as to project therefrom in a plane parallel to the screw 19. A fluid line 34 interconnects the hydraulic clylinders 33 and is connected to a hydraulic cylinder in a control unit 36 the details and operation of which will appear hereinafter.

The screw 19 has at one end thereof :a nut 37 in angularly fixed relation to the screw, the nut having a toothed sleeve 38 fixed thereto and embracing one end (Fig. 6) of a shaft 39. The toothed sleeve 33 cooperates with a correspondingly toothed sleeve 40 angularly fixed on the shaft 39 but axially slidable thereon to disengage the sleeve 38. As shown in Fig. 6, the sleeve 48 is urged by -a spring 41 against the sleeve 38. The shaft 39 is driven from a conventional gear reduction unit 42 connected to the output shaft of an electric motor 43. The arrangement is such that when the cooperating toothed sleeves 38, 40 are interengaged and the motor is energized, the motor 43 drives the screw 19. It will be understood that rotation of the screw 19, which may be very slow, effects movement of the nut member 30 axially of the screw. It will be further understood that lengthwise movement of the nut member along the screw in one direction effects movement of the fluid pressure devices 29 away from the lugs 28 while lengthwise movement of the nut member 30 in the other direction effects movement of the iluid pressure devices toward the lugs The fluid pressure devices 29 bear against the lugs 2S of the carriage to prevent movement of the carriage in a direction to cause slack in the belt i4 driven by the motor on the carriage. Moreover, the arrangement is such that when the tension on the belt de through belt stretch and differences in the load transmitted, for example, the pressure of the carriage lugs ZS on piston members 32 also decreases and causes a drop in fluid pressure behind the piston members. lt may be noted here that the fluid line 34 interconnects the hydraulic cylinders 33 at their ends remote from the carringe lugs lt will be understood that when pressure is reduced in the hydraulic cylinders 33 a change of pressure is effected in hydraulic cylinder 35 through the fluid line This change in pressure cilects actuation of the electric motor 453 (by means which will appear hereinafter) to drive the screw l@ and thereby move the nut member 3) to a position to restore the pressure of the devices 29 on the carriage lugs 23, and consequently restore the tension on the belt ld. Hence it will be understood that, in the present instance, movable motordriven pulley ll3 is, in effect, a belt-tensioning pulley. The motor 43 is automatically shut ofi when the pressure of the devices 29 on the carriage is restored, the arrangementr being such that a predetermined tension may be exerted on the belt which, through the automatic shut otf of the motor 43, is never exceeded. I will now describe the controls between the fluid pressure devices 29 and the electric motor As described above, the Huid line 3d interconnecting the iiuid pressure devices Z9 is connected to the hydraulic cylinder 3S. The hydraulic cylinder 35 has a piston member 45 extensible therefrom. A spring d6 at one side of the piston member 45 urges the piston member in a direction to retract the same when the fluid pressure decreases at the remote side of the piston member. As sho-wn in Fig. 2, the fluid line 3ft is connected to the cylinder 35 at the last-mentioned side ot the piston member. As shown in the last-mentioned view, the piston member 45 extends from the cylinder 35 and has at its outer end a ixed crosshead 47. As best shown in Fig. 7, one side of the cross head cooperates with a trip member 4S and the other side cooperates with a trip member 49. The trip members d8, may be of threaded spindle-like form and adjustable lengthwise in switches t? and Si, respectively. As indicated in Fig. 7, the arrangement is such that when the piston member 45 is extended a distance from the cylinder 35 the crosshead t7 engages `and operates trip 48 while retraction of the piston member a distance into the cylinder 35 operates trip 49. Switch 5t) is spring pressed to the closed position thereof and is held open by the crosshead e7 in the normal position of the latter shown in full lines in Fig. 7. in this position of the crosshead there is adequate uid pressure in the'devices 29 and adequate tension on the belt i4. However, when the tension on the belt decreases for some reason the carriage-supported pulley 13 shifts away from the pulley 13a and is followed by the piston members 32. This movement (see Fig. 7) of the piston members eects a lowering of fluid pressure behind them. This effects retraction of the spring- .pressed piston member d5 which, through the crosshead 47, first releases the trip 48 thereby permitting the switch Si? to close.

As shown in Fig. 7, current may not ow to the motor 43 until the switch 5l is also closed. This switch is normal-ly open, being spring biased to` the open position thereof. When the piston member 45 has `been retracted a distance sufficient to engage the trip 49 (see the brokenline position of the crosshead 47 in Fig. 7) the switch 51 is closed thereby permitting current to ilow through heater 53 and, through heater 53, to the motor i3 to energize the latter. From the foregoing it will be understood that operation of the motor eiects rotation of the screw i@ in a direction to restore the pressure of devices 29 against the lugs 28 of the carriage, and consequently build up liuid pressure behind the piston members 32 of the devices. Ythis build-up in pressure effects extension of the piston member 4S in the cylinder 35 thereby releasing trip so that switch 5l may open. After switch 5l is opened the llow of current through the heater 53 ceases and current flows instead through a by-pass 54 around the switch Si. The by-pass includes a birnetallic Contact 55 under the inlluence of the heater and which, after current ceases to flow through the heater, remains for a while in engagement with contact 56 so that current may continue to 'low to the motor However, when the crosshead d'7, carried by the piston memer 45, is extended a distance sufficient to engage and opt-rate the trip ib the switch 5h is opened and the circuit is broken so that the motor stops. ln this manner the pressure of the devices 2% on the motor carriage is restored, consequently restoring the tension on the belt 14.

As previously indicated, there is a lag in the operation of the motor 43 after the belt commences to slacken owing to the distance the piston member i5 must travel before closing the motor circuit. The lag is desirable in that it tends to inhibit continual intermittent operation of the motor 43. However, if desired, the threaded spindlelike trips It and 49 may be adjusted lengthwise to increase the lag or reduce it, perhaps to'the vanishing point. The movement of the carriage lugs 2S effected through slackening of the belt and prior to operation of the motor 43 is shown exaggeratedly in Fig. 7. ln this view, the initial positions of the carriage lugs 28 are shown in full lines and the positions of the lugs after slackening o the belt and prior to operation of the motor 43 are shown in broken lines. It will be understood that operation or the motor 43 shifts the carriage lugs 28 somewhat to the left of the broken-line positions shown in Fig. 7. To set up the belt-tensioning mechanism initially, it is only necessary to ydisengagc the toothed sleeve 40 from the toothed `sleeve 38 and then turn the nut 37 xed to the screw 11.9 until sulicient tension is exerted on the belt. The driving connection between the motor 43 and the screw i9 may then be restored by releasing the spring-pressed sleeve 40 permitting it to reengage the sleeve 38. The trip members 48, 49 may then be adjusted, if desired, to effect actuation of the screw-driving motor when a certain degree of slackness is caused in the belt.

From the foregoing disclosure it will be understood that there is provided a belt-tensioning mechanism having a fully automatic improved control system. The mechanism compensates for any slackness in the belt irrespective of the direction of rotation of the belt. Furthermore, the control system for the mechanism is extremely flexible and permits a number of adjustments. The belttensioning mechanism, including the controls, is not of a complicated nature and is reliable in operation and relatively inexpensive to produce.

While only one form of the belt-tensioning mechanism has been shown in the accompanying drawings and described above, it will be apparent to those skilled in the art that the belt-tensioning mechanism may take other forms and is susceptible to various modilications and changes in details without departing from the principles of the invention and the scope of the appended claims.

What I claim is:

l. In a belt-tensioning mechanism, a horizontally and rectilinearly movable carriage supporting a belt-tightening pulley, means for holding the carriage in a selected position to exert a predetermined tension on a belt trained over the pulley and including a bodily movable fluid.l

pressure device engaging the carriage, and means inc1uding a motor-driven screw mechanism for shifting the fluid pressure device bodily in a belt-tightening direction and operative on a decrease of iluid pressure in the device.

2. In a belt-tensioning mechanism, a horizontally and rectilinearly movable carriage supporting a belt-tightening pulley, fluid pressure means including a movable pressure device for holding the carriage in a selected position to exert a predetermined tension on a belt trained over the pulley, and means for shifting said device bodily in a belttightening direction in response to slackening of the belt and a lowering of iluid pressure in the rst-named means.

3. ln a belt-tensioning mechanism, a horizontally and rectilinearly movable carriage supporting a belt-tightening pulley, fluid pressure means including a movable pressure device for holding the carriage in a selected position to exert a predetermined tension on a belt trained over the pulley, and means for shifting said device bodily in a belt-tightening direction in response to slackening of the belt and a lowering of liuid pressure in the irstnamed means, the shifting means including a motordriven screw and an angularly fixed nut on the screw and carrying said pressure device.

4. In a belt-tensioning mechanism, a horizontally and rectilinearly movable carriage supporting a belt-tightening pulley, fluid pressure means including a pair of laterally spaced hydraulic cylinders having piston members extending therefrom and engaging the carriage, the piston members being extensible from the respective cylinders to hold the carriage in selected position to exert a predetermined tension on a belt trained over the pulley, motor-driven screw means for shifting said cylinders bodily in a belt-tightening direction, a third cylinder have ing a spring-urged piston member extending therein, the third cylinder being connected to a fluid line interconnecting the other two cylinders so that a decrease in pressure behind the piston members engaging the carriage effects movement of the spng-pressed piston member in the third cylinder, and means responsive to the lastnamed movement of the spring-pressed piston member for operating and shutting off the motor-driven screw means.

References Cited in the le of this patent UNITED STATES PATENTS 1,581,091 Stewart Apr. 13, 1926 1,730,319 Dilks Oct. 1, 1929 1,878,983 Harris Sept. 30, 1932 1,921,758 Koss Aug. 8, 1933 2,610,517 Hornbostel Sept. 16, 1952 

